An injection molding apparatus will have a manifold for delivering the plasticized melt from the injection unit to the mold cavity. The manifold will have a header and may have a number of drops, each having a valve gate for sequentially injecting and filling the mold cavity. As shown in FIG. 4, each valve gate 72 has a pin 74 that moves in the direction of the flow of plasticized melt to remotely open and close the valve and thus control the flow of the plasticized melt. U.S. Pat. No. 5,762,855 describes in detail an apparatus for injection molding utilizing sequential valve gating.
The pin arrangement of the prior art operates effectively for plasticized melt that do not include glass fibres. However, if the plasticized melt includes glass fibres, the pin location in the manifold drop creates an annular flow channel, reducing the effective flow area and increasing material pressure drop and shear, leading to glass fibre breakage. In addition, the tip of the pin creates additional shear on the material leading to further glass fibre breakage. Further, the operation of the pin in opening and closing the valve gate has a tendency to break the glass fibres and thereby reduce the effectiveness of the glass fibres as reinforcement of the finished molded part.
Thus, there is a recognized need to provide an apparatus for delivering plasticized melt incorporating long glass fibres to a mold cavity without seriously affecting material flow and damaging or breaking the fibres.